Usually test strips consist of an absorptive carrier material transporting the liquid to be examined, onto which carrier material one or more test zones have been applied, the test zones being, for example, shaped as lines and extending transversely across the width of the test strip and containing a reagent reacting with the substance to be detected in a detection assay, which assay usually consists in a change of the colour of the test zone and can therefore be measured optically. Moreover the test strip can be provided with a control zone situated in a spaced relationship behind the one or more test zones when viewed in the flow direction of the liquid to be examined. The control zone serves primarily to establish the progress of the wetting of the test strip by means of repeated amplitude measurements and to thereby trigger the start of the measuring action. If sufficient wetting is detected at the control zone it is after all safe to assume that the test zone located in front of the control zone in the flow direction has also been wetted sufficiently to provide a usable measuring signal. Moreover the measured values obtained at the control zone may also be used to determine the plausibility of the actual measurement results obtained at the test zone.
In actual practice it has been shown that the measurement curve obtained by moving the sensor arrangement over the test strip surface and at the same time measuring the reflected light also contains signals which are comparable with the actual measured signals in their amplitude but which are the results of disturbances, i.e. which are artefacts. Such artefacts may for instance occur when the measuring strip is covered with a transparent foil which causes undesired reflexes when irradiated with the measuring light. However artefacts may also be the result of impurities or inhomogenities in the measuring strip.
The invention has as its object to provide a method of the kind mentioned above which enables the detection of artefacts of the aforementioned kind in a simple manner.